Inorganic nitrate explosive



Patented Aug. 8, 1939 du Pont de Nemours & Company, Wilmington, Del., acorporation of Delaware No Drawing.

Application March 8, 1938,

Serial No. 194,551

24 Claims.

The present invention relates to the production of new and improvedexplosive compositions,

wherein ammonium nitrate or other suitable in-' organic nitrate is animportant ingredient, and relates particularly to an improved method ofsensitizing ammonium nitrate for use in such compositions.

Ammonium nitrate is widely employed as a constituent of explosives.While it is considered an explosive salt, it is too insensitive byitself to be initiated readily or to sustain propagation consistently.

The methods employed heretofore for the sensitization of ammoniumnitrate'to produce inorganic nitrate explosives have not been effectiveexcept as excessive amounts of 'sensitizer were used, undesirablysensitive materials were employed,-. dangerously high temperatures werenecessary for the operations, or other disadvantages were'introduced.

The object of the present invention is a new and improved inorganicnitrate explosive, in particular, an ammonium nitrate explosive! Afurther object is a process for the production of 25 an improvedexplosive in which ammonium nitrate or other inorganic nitrate is achief constituent. An additional object is a process for producingammonium nitrate explosives wherein highly intimate contact betweenammonium ni- 30 trate and sensitizer is obtained without the necessityof elevated temperatures. Other objects will be apparent from thedetailed description of my invention hereinaften I have found that theforegoing objects are accomplished by the process which comprisesdissolving ammonium nitrate or other ammoniasoluble inorganic nitrate insubstantially anhydrous liquid ammonia, dispersing in said solution asensitizer tor said nitrate, expelling the free 40 ammonia, and therebyforming a product in which the sensitizing material is dispersed in thesolid nitrate, the latter compound being a continuous phase.

A large number of inorganic and organic compounds and materials areadapted for use as sensitizing ingredients according to my invention,

such sensitizers being ordinarily either explosive compounds themselvesor compounds containing insuficient oxygen for complete combustion,

50 hence capable of utilizing the excess oxygen present in the ammoniumnitrate. I prefer to employ as a sensitizer an imperforate material,since the freedom from pores or cavities that is implied in this term.is a requisite. It is a dispersion of the sensitizer in the ammoniumnitrate which is desired and not saturation of the sensitizer with anammonium nitrate solution prior to solidification. With the use of suchimperforate sensitizers and the consequent presence of ammonium nitrateon the outside of the particles, the explosive possesses the severaladvantages of, (1) insensitiveness to shock and friction, and (2)improved sensitiveness to the detonation impulse, with (3) possibilityof wide variation of bulk strength. As examples of suitable imperforatesensitizers, I may cite such inorganic materials as aluminum, magnesium,antimony, zirconium, ferrosilicon, calcium silicide, sulfur, and thelike; in fact, any inorganic oxygen-accepior and sensitizer which isstable under atmospheric conditions and in the presence of ammoniumnitrate and ammonia.

Likewise, imperforate organic sensitizers are highly eflicient assensitizing agents according to my invention, and, as examples of suchcom-' pounds, I may cite amines such as diphenylamine, para-phenylenediamine, aniline hydrochloride, and the like; acid amides as exemplifiedby dicyandiamide, acetamide, oxamide, etc.; nitrocompounds such asmononitronaphthalene, di-" nitrotoluene, trinitrotoluene, dinitrophenol,trinitrophenol, tetryl, and the like; alcohols such as pentaerythritoland polyvinyl alcohols; aldehydes as reprmented by paraldehyde andbenzaldehyde; various sugars, for example sucrose; ammonium salts suchas ammonium formate and ammonium thiocyanates; and many others.

While I find it important to use an imperforate sensitizer, I find it iseven more advantageous to employ a sensitizer which is itself soluble inliquid ammonia, since extreme intimacy of contact between the ammoniumnitrate and sensitizer is thereby readily efiected. A large number ofthe organic materials named in the foregoing as imp'erforate materialsare soluble in liquid ammonia, and it is unnecessary to enumerate thesedesirable sensitiz'ers again. Such materials as diphenylamine, aniline,dicyandiamide, acetamide, trinitrotoluene, sucrose, and ammonium formatemaybe cited, however, as sensitizers soluble in anhydrous liquidammonia.

In addition to the soluble sensitizers, it will be understood thatimperforate mater'al insoluble in liquid ammonia are desirable for useand may be readily dispersed in solutions of ammonium nitrate or otherinorganic explosive salt .therein. The inorganic materials enumeratedunder the imperforate sensitizers are such examples and many insolubleorganic sensitizers are likewise desirable. As such insoluble,advantageous materials, I may cite mononitronaphthalene, pentaerythritoltetranitrate, and parafiln. A. highly emcient sensitization is alsoeffected by employing a sensitizer insoluble in liquid ammonia, togetherwith a dispersing agent, the latter being miscible with said ammonia. Asas example of this type, I may cite the use of dinitrotoiuene dispersedby means of the soluble trinitrotoluene, sulfur' dispersed by means ofsaponin, and many other insoluble sensitizers ly saturated with respectto ammonium nitrate.

The free ammonia of the solvent is then expelled by evaporation, withemployment of reduced pressure, if desired. The mass is preferablyagitated vigorously during the escape of the free ammonia. The solidmaterial resulting from this process may be described as a dispersionproduct in which extremely minute regions of the sensitizer aredisseminated within crystals of ammonium nitrate, the latter being thecontinuous phase.

It will be understood that the sensitizer may be one soluble itself inthe liquid ammonia, or it may be insoluble therein, or again may be oneof increased solubility or miscibility when first mixed with adispersion agent. In the latter case,

the substantially insoluble sensitizer is preferably thoroughly mixedwith the dispersion agent before addition to the liquid ammoniasolution,

desirably with agitation The following examples are illustrative of myinvention and give details sufllcient to enable anyone skilled in theart to practice said invention.

- Example 1 817 grams of'ammonium nitrate was placed in a one-litercontainer provided with two glass conduits, one for the introduction ofliquid ammonia, and the other for the venting of gaseous ammonia.Suflicient anhydrous liquid ammonia was introduced into this containerto dissolve the ammonium nitrate and form an approximately saturatedsolution of ammonium nitrate in liquid ammonia at 20 C. The saturatedsolution was introduced into a jacketed mixing vessel provided withmeans of agitation. 183 grams of finely divided aluminum was added tothe solution, with stirring. The vessel was closed to the atmosphere andthe free ammonia expelled by heating and evacuating the gas, whileagitating. The solution boiled freely until the temperature reachedapproximately-28 C., whe n solidification occurred. Upon subsequentheating of the system and further removal of the ammonia therefrom, thetemperature first fell to around10 C. and then rose to approximately 30C. At this point, the product was removed from the system, and consistedof ammonium nitrate in continuous phase; containing minute regions ofaluminum disseminated within said continuous phase.

Example 2 Example 3 I 100 grams of finely divided sucrose was dissolvedin 900 grams of ammoniumnitrate, in

The process was;

solution in liquid ammonia.

then carried out as described in Example 1. The product consisted ofammonium nitrate as a continuous phase, containing minute regions ofsucrose disseminated therein.

Example 4 100 grams of polyvinyl alcohol was incorporated in 900 gramsof ammonium nitrate by the process of Example 1. The product comprised avery intimate mixture of ammonium nitrate and polyvinyl alcohol, theammonium nitrate being present as the continuous phase.

Example 5 35 grams of hexamethylene tetramine was dispersed in.- 965grams of ammonium nitrate, in solution in anhydrous liquid ammonia. Theexplosive was then prepared in accordance with the process described inExample 1. The product consisted of finely divided particles ofhexamethylene tetramine disseminated throughout a continuous phase ofammonium nitrate.

Example 6 918 grams of ammonium nitrate was introduced into a jacketedgraining kettle equipped with agitation means. 82 grams of alphanitronaphthalene in molten form was then added and the mixer closed. 250grams of anhydrous liquid ammonia was then run into the graining kettleand agitation of the mixture was maintained until all the ammonianitrate was in solution. The free ammonia was then removed by heatingthe kettle to 30-35" 0., with final evacuation under reduced pressure.The agitation was continued throughout the drying, yielding a dry, looseproduct comprising minute regions of mononitronaphthalene disseminatedwithin crystals of ammonium nitrate.

Example 7 30 grams of crude trinitrotoluene was dissolved in- 70 gramsof dinitrotoluene at a temperature between 50 and C. Thissolution wasadded, while hot, to a solution of 900 grams of ammonium nitrate inanhydrous liquid ammonia. The dinitrotoluene by itself is difiicultlysoluble in the ammonia solution, but dispersion took place readily inthe .presence of the trinitrotoluene. The process was then continuedaccording to the method described in Example 1. The product consisted ofa continuous phase of annnonium nitrate containing minute regions oftrinitrotoluene and dinitrotoluene disseminated intimately therethrough.

The following table shows the detonating characteristics of sensitizedammonium nitrate compositions prepared according to the process of myinvention. These compositions were all sensitive to propagation by meansof a standard No. 6 commercial blasting cap.

Percent Percent Veloely Sensltlzer sensitize: $333 meters/secondAluminum l8. 3 8i. 7 2980 Sulfur 16. 0 84. 0 2000 Dicyandiamrde. l0. 090. 0 2860 Diphenylamine 6. 7 93. 3 2600 Polyvinyl alcohol 8. 8 91.22260 Sucrose. 10.0 90.0 2300 Hexamethvlenetetramine 8.9 91. l 3000Dinitrotoluene'. 7. 5 92. 5 1927 Trinitrotoluene 20. 0 80. 0 3500Mononitronaphtbalena. 8. 2 91. 8 1600 Tetry 29. 7 70. 3 4530p-Phenylenediamine 7. 8 92. 2 3010 'ItwiIl be appreciated that thevelocity values given in the table are merely illustrative and do notshow the relative or limiting values of the compositions, since noattempt was made to maintain uniform densities.

The ammonium nitrate sensitized according to my invention may beemployed as an explosive, either alone as tabulated, or mixed with othermaterial. Desirable blends may be produced from the sensitized materialwith other explosive material, ior example by the use of my sensitizedproduct with ordinary untreated ammonium nitrate or with ammoniumnitrate recrystallized .from liquid ammonia. The blends may be renderedcap-sensitive or not for a given density, as desired, by regulating theamount of sensitizer used or the amount of sensitized ammonium nitratein the blend. Very high strength values are obtained with the materialof my invention. Oxygen balance will be adjusted to the desired ,valueby control of the relative amounts of sensitizer and ammonium nitrate.

I find the type of explosive illustrated in Example to be a preferredand very advantageous form of my invention, where dinitrotoluene,dispersed by means of trinitrotoluene, is itself dispersed in theammonium nitrate in solution in anhydrous liquid ammonia. The followingtable shows the properties-of explosives so prepared, with varyingmethods of blending. It will be noted that sodium nitrate as well asammonium nitrate may be incorporated in the compositions by solution inliquid ammonia. While the tabulated compositions show sodium nitrateonly in explosives containing ammonium nitrate also, it

will be understood that sodium nitrate, or other of between 50 and 100m/sec. were observed for each per cent of material passing through said50-mesh screen. In other words, controlled reductions or increases invelocity in a velocity range never reached heretofore in ammoniumnitrate explosives, were obtained by controlling the degree ofcoarseness of the sensitized ammonium nitrate material so that apredetermined amount of fines passing through a 50-mesh screen waspresent. The velocity can be con trolled as well as by selectingsensitized ammonium nitrate of such a degree of coarseness that it willbe held on screens somewhat finer than said 50-mesh screen, the finenessof the screen and resulting fineness of material passed therethrough tobe determined in accordance with the particular velocity sought. #5 and#6 are compositions containing sodium nitrate, both (#5) mixed dry withdry explosive of my invention and (#6) with the sodium nitrate dissolvedlikewise in liquid ammonia. In the foregoing tabulation, thesensitiveness is expressed as the maximum air space, in inches, acrosswhich one cartridge will consistently detonate a second'cartridge withundiminished velocity of detonation. The latter property is expressed inmeters per second. Explosives of this type preferably will containammonium nitrate in an amount in excess of 85% and preferably between 88and 98%,

desirably with 4 to 8% dinitrotoluene, and 2 to 6% trinitrotoluene.

' The foregoing tabulations and examples are to be construed asillustrative and not limiting. Ammonium nitrate may be employed inamounts much less than 85% and, indeed, may be added in any convenientproportion. It may be added entirely by means of the ammonia process, or

Ingredients 1 2 Ammonium nitrate. Dinitrotoluene. Trinitrotoluene.Sodium nitrate Method of incorpora- 1 part coarse, dry

1 part sodium niil parts coarse KN- ti0l1- ammonium niadded to asaturdium ultra trate incorpotrate blended ated solution in blended withrated w1th9parts with 4 parts dry liquid ammonia 9 parts of #2 by theam- #2 composition. of a composition dry #2 commonia process.

. approximating #2. position.

(9 parts) ammonia then expelled Density:

Ctgs./50 lbs 13 148. Sensitive n e s s t o 3-9",

propagation. Velocity, m/sec 3480.

The foregoing tabulation is illustrative of my process and theproperties of the. compositions prepared thereby. The advantages of theammonia process are shown strikingly by comparison of #2 and #1. Ihecompmition which failed to shoot when incorporated by simple dry mixtureshowed excellentexplosive properties when blended by the liquid ammoniaprocess. Whereas the use of the ammonia process of incorporation gave aless dense powder than the simple mixture of #1, the addition of coarseammonium nitrate, that is, material of such particlesize'that thegreater part will pass a 35-mesh screen but will be held on a fill-mesh,brought again the dense product shown in #1. #4 illustrates a very lowvelocity explosive of reasonably satisfactory sensitiveness, which wouldbe very advantageous for certain types of blasting. Approximatelyminimum velocity was obtainedwlth material wherein substantially none ofthe sensitized ammonium nitrate passed through a 50- Increases invelocity to the'extent mesh screen.

ployed heretofore.

monia process allows the production .of a dry,

'tures.

in part by blending additional amounts of the salt with any .of theproducts of the ammonia process.

Likewise, the amount of sodium nitrate need not be limited to 10%, asshown-in the tabulation, but may be employed either alone or withammonium nitrate or other ammonia soluble in-- organic nitrate in widelyvarying amounts. For instance, the sodium nitrate or other inorganicnitrate may be present as of the entire composition, for example.

Numerous advantages are gained by operation according to my invention,since it provides a safer, more rapid, and more eflicient method ofsensitizing ammonium nitrate to produce ammonium nitrate explosives thanthe methods em- In the first place, my arm desirably sensitive materialwithout the employment of other than relatively low tempera- Hence, nohazard is possible from this source. In my ammonia process, the solventaction of ammonia on ammonium nitrate is very rapid, even at lowtemperatures, and relatively high concentrations of ammonium nitrate areobtainable at pressures below one atmosphere. Furthermore, hightemperature is unnecessary for driving ofi the free ammonia after ahomogeneous product has been formed. It is a remarkable characteristicof solutions of ammonium nitrate in liquid ammonia that, atapproximately 28 C., a solution of around 20% ammonia and 80% ammoniumnitrate becomes solid, and remains so at all higher temperatures, thoughstill containing an appreciable amount of ammonia. The remainder of theammonia can be removed and recovered completely, either by evacuation orapplication of heat, or by a combination of both methods. A relativelylow temperature such as C. is sufllcient, for example, at one atmospherepressure. Using such temperatures, no danger is involved of thermaldecomposition of the sensitized material.

An important advantage of my ammonia method of sensitization lies in thefact that a much more intimate dispersion of the sensitizer particles isachieved than has heretofore been possible, with the result that a muchsuperior product is obtained. The properties of liquid ammonia that makepossible its ready removal, when desired, assure the maintenance of theintimate contact of sensitizer and ammonium nitrate.

It is further characteristic of compositions according to my inventionthat the tendency to set or become hard on storage is greatly reducedover that of ammonium nitrate compositions where crystallization hasbeen from water.

When incorporated with ammonium nitrate by the ammonia process,sensitizers soluble or dispersible in liquid'ammonia give productssensitive to initiation by a standard commercial blasting cap, with amuch lower percentage of sensitizer than is necessary to produce thatresult with products of other methods. In addition, a number ofmaterials which fail to produce cap-sensitive compositions whenincorporated in ammonium nitrate by the methods of the art, givecapsensitive products when incorporated by the ammonia process.

A further desirable feature of the ammonia process of sensitization lies"in the fact that sensitiveness of ammonium nitrate to intentionalinitiation is enhanced, without rendering the material increasinglysensitive to shock, friction, or flame. It is known that sensitizedammonium nitrate compositions produced by other methods seem to partakeof the qualities of the sensitizer employed, so far as shock, friction,and flame are concerned. My compositions, however, are

approximately as insensitive in this respect as pure ammonium nitrate.While compositions of sensitized ammonium nitrate prepared by my processare less sensitive to shock, friction, and accidental means ofinitiation, they are, as a matter of fact, more readily initiated byblasting caps or other controlled detonating influence than compositionsprepared by other methods.

The fact that the compositions according to my invention are insensitiveto shock and friction not only makes them attractive from a safetystandpoint during manufacture, packaging, and charging operations, butalso removes the hazards which normally accompany the occurrence ofmisflres in the borehole. When a misflre occurs, the drill may beinserted in the hole and the powder drilled out along with the tamping,

without danger of explosion. The cap should, of

course, first be removed from the hole, after a misfire.

Explosive compositions having an extremely high velocity may be readilyproduced by my process. -Unexpectedly, however, this velocity does notfall off rapidly with increase in density as is the case with otherammonium nitrate explosives. This permits pelleting of the powders to ahigh bulk strength even in small diameters, without extreme loss insensitiveness.

Throughout this specification, the emphasis has been placed on ammoniumnitrate compositions prepared by the ammonia process. It should beunderstood, however, that my invention is likewise applicable toexplosives containing sodium nitrate, potassium nitrate, calciumnitrate, or other inorganic nitrate soluble in anhydrous liquid ammonia,and blended with a sensitizing material by use of said solvent.

For some purposes it has been found useful to replace a portion or allof the ammonium nitrate with one or more of the other ammonia solubleinorganic nitrates. For example, the strength of a given ammoniumnitrate composition, as prepared by the ammonia process, may be loweredor controlled by the addition or substitution of a portion of sodiumnitrate or other ammonia soluble inorganic nitrate. These other nitratesmay be added either by introduction into the ammonia process or byblending amounts of said nitrates with material already sensitized inthe ammonia process. In this manner a wide range of explosive strengthsmay be achieved with the use of much smaller amounts of ammonia nitrateitself. j

In the present specification and the subsequent claims, I havedesignated the type of desirable sensitizer as imperforate. Itwill beunderstood that this ,term describes a normally solid material which is'substantially and characteristically free from pores, cavities, andinternal crevices, when in solid form.

As many apparently different embodiments of this invention may be madewithout departing from the spirit and scope thereof, I intend to beammonium nitrate as a continuous phase, in

which minute regions of an imperforate sensitizer are disseminated, saidsensitized ammonium nitrate possessing non-setting properties astheresult of crystallization from substantially anhydrous liquid ammonia.

3. An ammonium nitrate explosive comprising a solid dispersion ofammonium nitrate and a comminuted imperforate sensitizer, saiddispersion resulting from crystallization from solution in substantiallyanhydrous liquid ammonia.

4. An ammonium nitrate explosive comprising a solid solution of ammoniumnitrate and an ammoniasoluble sensitizer, said solution resulting fromcrystallization from solution in substantially anhydrous liquid ammonia.

5. An ammonium nitrate explosive which comprises 88 to 98% ammoniumnitrate, 4 to 8% dinitrotoluene, and 2 to 6% trinitrotoluene, saiddinitrotoluene and trinitrotoluene being inti- 'mately disseminatedwithin the crystals of ammonium nitrate as the result of dispersion bymeans of crystallization from substantially anhydrous liquidammonia.

6. The process of producing an inorganic nitrate explosive, whichprocess comprises dissolving said inorganic nitrate in anhydrous liquidammonia, dispersing in said solution a comminuted imperforate sensitizerfor said inorganic nitrate, and vaporizing the free ammonia to produce asolid dispersion product wherein the inorganic nitrate is a continuousphase.

"7. The process of preparing an inorganic nitrate explosive, whichcomprises dissolving said inorganic nitrate in substantially anhydrousliquid ammonia, dispersing in said solution a comminuted imperforatesensitizer for said inorganic nitrate, and expelling the free ammoniatherefrom.

8. The process of preparing an ammonium nitrate explosive whichcomprises dissolving ,ammonium nitrate liquid ammonia, dispersing insaid solution a comminuted imperforate sensitizer, andexpel-'- ling thefree ammonia therefrom.

9. The process of preparing an ammonium nitrate explosive whichcomprises dissolving ammonium nitrate in substantially anhydrous liquidammonia, dispersing in said solution a comminuted imperforate inorganicsensitizer, and expelling the free ammonia therefrom.

10. The process of claim 9, in which the inorganic sensitizer isaluminum.

11. The process of claim 9, in which the inorganic sensitizer issulphur.

12. The process of claim 9, in which the inorganic sensitizer isferrosilicon.

13. The process of preparing an ammonium nitrate explosive whichcomprises dissolving ammonium nitrate in substantially anhydrous liquidammonia, dissolving a soluble sensitizer therein, and expelling the freeammonia therefrom. I

14. The process of preparing an ammonium nitrate explosive whichcomprises dissolving ammonium nitrate in substantially anhydrous insubstantially anhydrous:

liquid ammonia, dissolving in'said solution an organic sensitizersoluble in liquid ammonia, and expelling the free ammonia therefrom.

15. The process of claim 14, in which the soluble organic sensitizer issucrose.

16. The process of claim 14, in which the soluble organic sensitizer istrinitrotoluene.

17. The process of claim 14, in which the soluble organic sensitizer isdicyandiamide.

18. The process of preparing an ammonium nitrate explosive whichcomprises dissolving ammonium nitrate in substantially anhydrous liquidammonia, dispersing in said solution a comminuted imperforate organicsensitizer, and expelling the free ammonia therefrom.

19. The process of claim 18,.in which the insoluble organic sensitizeris pentaerythritol tetranitrate.

20. The process of claim 18, in which the insoluble organic sensitizeris paraffin,

21. The process of claim 18, in which the insoluble organic sensitizeris mononitronaphthalene.

22. The process of preparing an ammonium nitrate explosive, whichcomprises dissolving ammonium nitrate in substantially anhydrous liquidammonia, disseminating an imperforate sensitizer in said solution withthe aid of a dispersing agent, and expelling the free ammonia therefrom.

23. The process of preparing an ammonium nitrate explosive, whichcomprises dissolving ammonium nitrate in substantially anhydrous liquidammonia, disseminating therein an imperforate aromatic nitrocompoundsubstantially insoluble in liquid ammonia by dispersion of saidinsoluble nitrocompound with an aromatic nitrocompound soluble in liquidammonia, and expelling the free ammonia therefrom.

24. The process of preparing an ammonium nitrate explosive, whichcomprises dissolving ammonium nitrate in substantially anhydrous liquidammonia, disseminating dinitrotoluene therein by dispersion by means oftrinitrotoluene, and expelling the free ammonia therefrom.

CLYDE OLIVER DAVIS.

